Resonance chamber for pianos



1942. E. a. JONES RESONANCE CHAMBER FOR PIANOS 2 Sheets-Sheet 2 Filed Oct. 16, 1940 Patented Jan. 6, 1942 UNITED STATES PATENT OFFICE RESONANCE CHAMBER FOR PIANOS Edgar B. Jones, Oregon, 111. Application October 16, 1940, SerialNo. 361,367

'7 Claims.

This invention relates to a resonance chamber for pianos, and more particularly concerns the provision of a device of such character designed to be placed over the piano strings to supply additional tonal resonance for notes of certain portions of the scale where the resonance characteristics of the sounding board are deficient.

The principal object of the invention is to improve the tonal balance of the piano scale and to amplify certain desired tonal fundamentals and harmonics or note-partials, and an additional and important object is to provide a device of the aforesaid character constructed as a unit separate from the sounding board and designed to be adjustably positioned with relation to the piano strings, after tuning and tone-regulation thereof, if desired, to facilitate proper application and regulation of the responsive action of the unit in obtaining the desired tonal effects.

In the drawings,

Figure l is a view in front elevation of the lower portion of an upright piano provided with my resonance chamber, the lower front panel of the instrument having been removed to illustrate the arrangement of the chamber with respect to the piano strings;

Figure 2 is a fragmentary fore-and-aft vertical sectional View, taken upon the line 2-2 of Figure 1;

Figure 3 is a horizontal sectional View, taken upon the line 33 of Figure 1;

Figure 4 is a front view, partly in elevation and partly in vertical section, of one embodiment of my invention;

Figure 5 is a vertical cross-sectional view, taken upon the line 55 of Figure 4;

Figure 6 is a view similar to Figure 4 of another embodiment of my invention; and

Figure '7 is a vertical cross-sectional View, taken upon the line 'l--'! of Figure 6.

While my resonance chamber is qualified for use with all types of pianos to improve and amplify the tonal characteristics thereof and, when constructed and employed in the manner I shall describe, may be used therewith for all of the purposes for which it is designed, I have shown and shall describe it as applied to an upright piano, since the present popular demand for structurally low types of upright pianos has resulted in such shortening of the strings and sacrifice of sounding board area as to render my invention especially useful in connectiontherewith.

In pianos of the overstrung type, the strings of the overstrung or bass section of the scale are arranged to cross over the strings of the middle 55.

section and are attached by hitch-pins to the string-plate very close to the edge of the frame, in order to have them as long as the size of the instrument will permit. With such an arrangement, the sounding board bridge for the bass strings, commonly termed the bass string bridge, extends so near to the solidly supported lining strip edge of the sounding board that it is the general practice to undercut the bridge and secure the foot thereof upon the board as far from the edge of the board'as is practicable, so that some degree of sounding board resonance may be obtained for the lower notes of the scale. This offsetting of the foot of the bass string bridge and its necessary placement so near the solidly supported edge of the sounding board substantially reduces the resonant action of the board with respect to the overstrung or bass strings, since the vibrations of these strings are thereby transmitted indirectly to the board and to a portion thereof which is stiff in action and therefore less responsive than the portions upon which the greater part of the main string bridge is secured. Another fundamental cause for the loss of tonal quality in the notes of the bass section is that, with the shortening of the strings, it is customary to increase the weight of the winding with which each string is loaded to slow up its otherwise natural period of vibration sufliciently to produce the desired pitch.

It is well known by those familiar with piano construction that these practices may be carried out to a certain degree, beyond which, in the first described instance, the overhang of the bass bridge will absorb the string vibrations and fail to transmit them to the sounding board, and will act as a lever upon which the down-bearing of the strings will tend to pry and break the foot of the bridge from the board, and, in the second described instance, the loading of the shortened strings will render them so stiif as to cause them to partake of the nature of bars or rods, in which the whole-length vibrations of the strings are practically lost, and the fundamental tones cannot be heard until the vibrations of the tonal partials have subsided, producing what are commonly known as false notes.

As I have hereinbefore stated, the popular demand for low upright pianos has resulted in such shortening of the string scale as to render my invention particularly valuable in pianos of this type, but the same shortening of string scale and sacrifice of sounding board area has occurred in small grand pianos, and when applied to either type of instrument, the action of my resonance chamber is to furnish additional resonance and amplification to make up for the deficiencies of the sounding board and to bring out the fundamental tones of the bass section of the strings.

I am aware that various forms of sounding boards and resonance devices have been proposed for direct attachment to the main sounding board or for connection therewith by soundposts, but my resonance chamber differs from these in that it possesses its own resonance and amplifying characteristics which are wholly additional to those of the sounding board, are not dependent thereupon, do not interfere therewith, and are not interfered with thereby.

In Figure 1 of the accompanying drawings, I have shown sufficient structural elements of an upright piano to illustrate the application of my resonance chamber thereto. In an upright piano, as here shown, wherein the strings are arranged to extend in substantially vertical planes, the arrangement of my resonance chamber over the strings results in having it in front of them. When employed in a grand piano, wherein the strings extend horizontally, the arrangement of my resonance chamber over the strings results in having it above them. It will be understood, therefore, that in either case, the piano strings extend between my resonance chamber and the sounding board. Furthermore, for convenience in describing the construction of the chamber, I shall refer to the flat side thereof farthest from the strings as the outer wall and to the flat side nearest the strings as the inner wall.

Returning, now, to Figure l of the drawings, I

indicates the front of the manual keyboard; 2,-

the key-bed or table, upon which the keyboard is supported; 3, the toe-rail; and 4, the piano pedals. 5 is the lower portion of the sounding board, which extends the full width of the instrument and to the bottom thereof, and is glued to the bottom lining-strip 6 (Figure 2), which is in turn glued to the horizontal member 1 of the heavy back frame of the instrument. As herein shown, the lower portion of the solid cast metal stringplate extends to the bottom of the instrument, but not the full width thereof.

The lower ends of the strings of the treble and middle sections are attached by hitch-pins 8 and 9, respectively, to the plate-web I which extends obliquely downward from the upper portion of the plate at the treble side of the instrument to the bottom of the plate at the bass side of the instrument, where it joins the horizontal bottom plate-web II. The lower portions of four plate bars or ribs are shown at I2, I3, I4 and I5, all

of which reach from the upper portion of the plate to the bottom web II. Rib l2 extends parallel with the lowest string of the middle section; rib I3 extends parallel with the lowest string of the overstrung or bass section,joins with and forms an X with rib I2, and the lower portion thereof bridges over the lower strings of the middle section and joins the web II at about the middle thereof; rib I4 extends downwardly between the strings of the middle and treble sections, joins web I0, and then continues obliquely downward therefrom, parallel with the upper string of the overstrung or bass section, and joins rib I5 just above web I I; and rib I5 extends vertically downward from web Ill to web II.

The strings of the overstrung or bass section cross over the lower portions of the strings of the middle section, and their lower ends are attached by hitch-pins I6 to a cross-bar I! which extends obliquely downward for about half its length from the lower end-part of rib I4 and then along the bottom edge of web II to rib I3. This angular bend to the horizontal of the lower portion of cross-bar I1 is a graphic illustration of how the reduction in the height of the instrument and the consequent reduction in the height of the plate has resulted in the shortening of the lower strings of the bass section. A rim-flange I8 (Figure 2) is formed along the entire bottom edge-part of the plate and is secured firmly down upon the bottom edge-part of the sounding board by heavy screws I9 which are passed at intervals through rim-flange I 8, sounding board 5, and lining strip 6, into the horizontal frame-member I.

While the treble and bass side edge-parts of the sounding board are firmly secured upon respective side lining strips (such as indicated at 20 in Figure 2) and to the heavy back frame of the instrument in the same manner as the bottom edge-part, the screwing down of the cast metal plate upon the bottom edge-part of the board adds to the rigidity with which this part of the board is held. Consequently, there can be no vibration of the board along its bottom edgeportion and the board is rendered stiff for a considerable distance inwardly from the rigidly fixed edge-portion, so that its resonant characteristics are deficient. To be more explicit, such vibratory qualities as are possessed by the stiffened lower portion of the board are limited to the higher frequencies of the harmonics or tone-partials of the lower strings and cannot respond to the lower frequencies of the fundamental tones thereof. That this fact has been appreciated is evidenced by the construction and arrangement of the lower end-part of the main string bridge and of the bass string bridge.

It will be observed that the main string bridge 2| is arranged upon the sounding board just above and along the hitch-pin Web ID of the plate and that the lower end-part of this bridge is curved away from the lower edge-portion of the board. It is at this curve that the shortening of the string scale and the use of wound strings begins. It has been stated that it is the general practice to undercut the bass string bridge and secure the foot thereof upon the board as far from the edge of the board as is practicable, so that some degree of sounding board resonance may be obtained for the lower notes of the scale. The bass string bridge 22 shown in Figure 1 is so constructed and secured, the string-bearing portion being indicated by the reference numeral 23 and the offset foot-portion by 24. The decided increase in the width of this string bridge 22 toward its bass end illustrates the aim of the manufacturer to have the vibratory portions of the lower strings of the overstrung bass section as long as the height of the instrument will permit and yet secure the foot of the bridge upon the board as far as practicable from the rigidly secured bottom edge-portion thereof in order to obtain some degree of sounding board resonance for these strings, but it also illustrates the decided overhang thus given to the bass end-portion of the bridge, which results in a considerable amount of the string vibrations being absorbed by the bridge and not transmitted to the board, in a much reduced capability of the bridge to transmit the low frequencies of the fundamental tones of the lower strings, and, because of the aforesaid stiffness in action of this lower portion of the board, the incapability of the board to properly respond to such low frequencies as may be trans mitted thereto.

My resonance chamber is designed to resonate sympathetically to the frequency vibrations of the fundamental tones and simple harmonics or tone-partials of the lower notes of the scale, and is intended to be used to compensate for the hereinbefore described deficiencies of the sounding board in this respect and improve the tonal balance of the instrument by contributing its resonant and amplifying qualities to that portion of the note scale most in need thereof. Furthermore, its position in the instrument with respect to the deficient lower portion of the sounding board is such that its resonant and amplifying action blends into and supplements the action of the board Without producing any noticeable break in the continuity of the tonal balance of the note scale. The chamber is so constructed and provided with openings that it may be supported separate from the sounding board with the openings presented to portions of the strings where the fundamental and simpler harmonic string vibrations are more pronounced and effective than at the string bridge and at the lower portion of the sounding board where the bridges for the lower strings are positioned and secured.

The chamber constitutes a comparatively shallow box, having an inner flat wall 25 and an outer crowned or bellied wall 23 secured about their entire edge-portions to the opposite faces of an irregularly shaped hollow frame which, in the present embodiment of my invention, is formed with a straight side wall 21, relatively long and short end walls 28 and 29, respectively, and a curved side wall 38. Supporting lugs 3| and 32 are formed as end extensions of the side wall 21, and these lugs are respectively provided with slots 33 and 34, through which screws 35 and 36 are passed and screwed into the plateribs l3 and M to secure the chamber firmly in position over the strings of the overstrung or bass section without interfering with the resonant or vibratory action of the body of the chamber. The end walls 28 and 29 extend obliquely from the straight side wall 21, so that, when the chamber is in position in the instrument, as shown in Figure 1, the longer wall 28 will be parallel with rib l3 and the larger endpart of the chamber will be over the lower strings of the overstrung section, and the shorter wall 29 will be parallel with rib l4 and the smaller end-part of the chamber will be over the upper strings of the section. It may be mentioned at this point that the peculiar shape of the chamber, including the curvature of the side wall 30, is the result of considerable experiment to obtain the desired balance in the resonance and amplification characteristics of the chamber for use with a selected string scale and plate construction, and, while the same general principles of construction are employed for use with other string scales, the proportions of the chamber may differ, and I do not wish to be limited to the exact form herein shown.

The inner flat wall 25 is provided with a series of openings 31, located in this example near the curved side wall 38. The number and size of these openings are designed to permit the chamber to pick up and respond to the desired vibrations of the strings without weakening the structure or sacrificing the resonant and amplification qualities thereof. Consequently, I prefer not to provide an opening 31 for each note of the scale represented by the respective strings, but to limit the number and sizes of the openings and so position them with relation to the strings as to obtain the desired balance in the action of the chamber with respect to all of the strings of the section. A series of sound-emission openings 38 is arranged in the outer crowned or bellied wall 26, shown herein as f-holes, near the straight side wall 21. The exact shape and number of these openings 38 are not of particular importance, but their position should be as far as practicable from the openings 37 in order to obtain the full resonant qualities of the chamber and their combined area should be such as not to sacrifice such qualities. A sound-post 39 (Figures 4 and 5) is firmly wedged and secured in position between the fiat wall 25 and the curved or bellied wall 26 near the middle of the chamber. In some instances, it may be desirable to reverse the arrangement of the two series of openings 31 and 38, placing the openings 3'! near the side 21 and the openings 38 near the curved side 30, depending to a large extent upon the character of the tone to be amplified and the convenient arrangement of the chamber in the instrument. The present arrangement has been found to give the desired results under the circumstances herein described, but here again I do not consider my invention as limited to the exact arrangement I have shown.

In the modification illustrated in Figures 6 and '7, the construction of the chamber is the same in all respects as that described and shown in Figures 4 and 5, with the exception that the sound-post 39 is omitted and an inner baffle 40 is employed to render the chamber resonant to higher frequency vibrations. Baflle 40 is arranged as an intermediate shelf in a plane parallel with that of the inner flat wall 25, securely joined to or in the curved wall 30 and the end walls 28 and 29, and with its free edge 4| extending parallel with the straight side wall 21 but spaced therefrom sufficiently to preserve as far as possible the overall resonance of the chamber for the lower frequencies and not cut off the action of the sound-emission openings 38. So that the bafiie 43 may serve its intended purpose and yet not cut off the overall resonance and amplification characteristics of the chamber to an undesirable extent, it is provided with a series of openings 42 arranged, as herein shown, in line with the series of openings 31 but in staggered relation thereto.

Having fully described my invention, I claim:

1. In a piano, the combination, with the piano string-frame and a series of strings arranged thereupon to extend in a common plane, of a resonance chamber supported upon said stringframe over said series of strings, said chamber constituting a box having an inner fiat wall extending in a plane proximate to and parallel with the plane occupied by said series of strings, said chamber being provided with a plurality of openings through said inner fiat wall.

2. In a piano, the combination, with the piano sounding board, the piano string-frame, and a series of strings arranged upon said string-frame to extend over said sounding board, of a resonance chamber supported upon said string-frame free from said strings and said sounding board and extending across said series of strings upon the opposite side thereof from said sounding board, said chamber constituting a box having an inner flat wall provided with openings therethrough and extending over said series of strings with the openings therethrough positioned over freely vibrating portions of said strings.

3. In a'piano, the combination, with the piano sounding board, the piano string-frame, a stringbridge secured upon said sounding board, and a series of strings arranged upon said string-frame and bearing upon said string-bridge, of a resonance chamber supported upon said string-frame free from said sounding board, strings and stringbridge and extending across said series of strings upon the opposite side thereof from said sounding board, said chamber constituting a box having an inner fiat wall provided with openings therethrough and extending over said series of strings with the openings therethrough positioned over vibratory portions of said strings at a selected distance from said string-bridge.

4. In a piano, the combination, with the piano string-frame and a series of strings arranged thereupon to extend in a common plane, of a resonance chamber comprising a hollow frame having two side walls, an inner wall and an outer wall secured about their respective edgeportions to opposite faces of said frame to constitute therewith a shallow box, said inner wall having openings therethrough near one of said side walls of said frame and said outer wall having openings therethrough near the other of said side walls of said frame, and means supporting said chamber upon said string-frame to extend across said series of strings with said inner wall occupying a plane proximate to and parallel with the common plane occupied by said series of strings.

5. In a piano, the combination, with the piano sounding board, the piano string-frame, a stringbridge secured upon said sounding board, and a series of strings arranged upon said stringframe to extend in a common plane and bearing upon said string-bridge, of a resonance chamber comprising a hollow frame having a straight side wall and a curved side wall, an inner wall and an outer wall secured about their respective edge-portions to opposite faces of said frame to constitute therewith a shallow box, said inner wall having openings therethrough near the curved wall of said hollow frame and said outer wall having openings therethrough near the straight wall of said hollow frame, and means supporting said chamber upon said string-frame to extend across said series of strings with said inner wall occupying a plane proximate to and parallel with the common plane occupied by said series of strings and with the curved side wall of said hollow frame arranged nearer said string-bridge than the straight side wall thereof.

6. In a piano, the combination, with the piano string-frame and a series of strings arranged thereupon to extend in a common plane, of a resonance chamber comprising a hollow frame having two side walls, an inner wall and an outer wall secured about their respective edge-portions to opposite faces of said frame to constitute therewith a shallow box, said inner wall having openings therethrough near one of said side walls of said frame and said outer wall having openings therethrough near the other of said side walls of said frame, a sound-post in said chamber connecting said inner and outer walls, and means supporting said chamber upon said stringframe to extend across said series of strings with said inner wall occupying a plane proximate to and parallel with the common plane occupied by said series of strings.

7. In a piano, the combination, with the piano string-frame and a series of strings arranged thereupon to extend in a common plane, of a resonance chamber comprising a hollow frame having two side walls and two end walls, an inner Wall and an outer wall secured about their respective edge-portions to opposite faces of said frame to constitute therewith a shallow box, said inner Wall having openings therethrough near one of said side walls of said frame and said outer wall having openings therethrough near the other of said side walls of said frame, a baflle in said chamber extending entirely across said chamber between and secured to the two end walls of said frame and extending partially across said chamber between the two side walls of said frame and secured to one thereof, and means supporting said chamber upon said string-frame to extend across said series of strings with said inner wall occupying a plane proximate to and parallel with the common plane occupied by said series of strings.

EDGAR B. JONES. 

